Abstract

Have you ever enjoyed eating a tasty sweet potato? They can be served as yummy mashed sweet potatoes with melted butter, turned into golden-brown sweet potato fries, or prepared in many other scrumptious ways. Did you know that you can make a sweet potato grow into a sweet potato plant, and grow several sweet potatoes this way? In this science project, you will grow your own sweet potato plants and investigate what part of the sweet potatoes is needed to grow the plants.

Objective

Investigate what part of the sweet potato is needed to grow a sweet potato plant.

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Introduction

If you want to grow tomatoes, watermelon, corn, or most other crops, you plant the right seeds. So what do you plant when you want to grow sweet potatoes? The answer is usually not a seed, but another potato! A sweet potato, like the one shown in Figure 1, below, is itself a tuberous root. A tuberous root is a type of plant root that becomes big because it is storing nutrients. Plants make tuberous roots so that they can have nutrients when conditions are not good for them to grow, such as during the cold winter season.

Under the right conditions, a sweet potato will sprout green shoots, leaves, and tiny, thin roots, as shown in Figure 2, below. These sprouts are called "slips." One sweet potato can grow many slips. Each slip can be removed by twisting it off of the sweet potato and then grown into a whole new sweet potato plant that is able to make more sweet potatoes! Sweet potato plants are vines that are related to flowering plants called morning glories.

Figure 2. A sweet potato growing slips.

In this science project, you will investigate what part of the sweet potato is needed for it to sprout slips. Figure 2 shows slips growing from a sweet potato with both skin and the inside flesh. Is a sweet potato's skin needed for it to sprout slips or is the inside flesh enough? To find out you will peel the skin off of some sweet potatoes, but leave other sweet potatoes intact. Will they all grow slips? Get ready to grow some sweet potato plants to find out, but you will need to be patient because it can take several weeks for the slips to grow!

Terms and Concepts

Tuberous roots

Shoots

Leaves

Sweet potato slips

Questions

How are sweet potato slips made?

What part of the sweet potato plant is the sweet potato?

How are sweet potato slips made into sweet potato plants?

Bibliography

Visit this website to learn more about how sweet potato slips are grown:

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Materials and Equipment

Large sweet potatoes (3)

Knife

Cutting board

Potato peeler

Metric tape measure or ruler

Toothpicks (at least 18). You will want to use colored toothpicks or you will also need a marker.

Cups (6). They should be at least 18 oz. in size, or large enough that the narrow part of the sweet potato can fit in the cup.

A warm, sunny window

Figure 3. To do this science project, you will need the materials shown here as well as a total of three large sweet potatoes.

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Experimental Procedure

Get an adult to help you carefully use a knife and cutting board to cut all three of the sweet potatoes in half. Cut them in half width-wise, as shown in Figure 4, below. Keep the halves paired together so that you know which halves originally went together to make each sweet potato.

Figure 4. Cut all three sweet potatoes in half, as shown here.

Next have an adult help you carefully use the potato peeler to peel one half of each pair. Peel the half so that it is about 0.5–1 cm smaller (in diameter) all over compared to the un-peeled half. Try to peel it the same amount all around, and make sure no skin is showing. See Figure 5, below, for an example.

Figure 5. Peel one half of each sweet potato so that it is about 0.5–1 cm smaller (in diameter) compared to the other half.

Push 3 or 4 toothpicks into each sweet potato half, putting each toothpick about 3 cm up from the cut-off part and evenly spacing them around the sweet potato, as shown in Figure 6, below. For each pair of halves, use the same-colored toothpicks to help you keep track of which halves make up the same sweet potato. Assign a number to each sweet potato (1–3) and, in your lab notebook, write down which number goes with each toothpick color.

Alternatively, if your toothpicks are all the same color, you can use a marker to make marks on the toothpicks (such as making several lines or coloring the entire toothpick) to help you match the halves. Be sure to still assign each sweet potato a number and write down which number goes with which toothpicks.

Put each sweet potato half in a cup so that the cut-off part is sitting facing down in the cup, as shown in Figure 6.

Figure 6. Put 3–4 toothpicks into each sweet potato half so that it can sit in a cup as shown here, with about 3 cm of each half sitting in the water in the cup.

Place the cups indoors near a warm, sunny window and fill each cup to the very top with water.

Leave the sweet potato halves by the window for at least ten weeks. Make sure the sweet potato halves are always touching water in the cup during your experiment. Make a data table, like Table 1, below, in your lab notebook to record your observations every 3–5 days. Remember that it can take several weeks for slips to sprout, so you will need to be patient!

Check on the water in the cups every 3 days. When the water level gets low and a sweet potato half is almost not touching it, carefully take out the sweet potato half, rinse the cup with clean water, put the sweet potato half back in its cup, and fill the cup back up to the very top with fresh water.

If a sweet potato half seems to have become rotten (in other words, it becomes soft, becomes darker in color, and looks like it is growing mold or fungus), you can throw it out (or compost it). Be sure to write down that you did this, along with your observations, in your data table. Do not worry if some of the halves become rotten — this is not unusual.

When you make your observations, look carefully all around on the sides of the sweet potato for shoots sprouting, and on the underside of the sweet potato for thin roots sprouting. Write down when you see shoots, roots, or leaves appear. Again, be patient — it may take several weeks for shoots to appear!

Observations

Sweet Potato

Sweet Potato Half

Date:

Date:

Date:

etc.

1

Not peeled

Peeled

2

Not peeled

Peeled

3

Not peeled

Peeled

Table 1. In your lab notebook, make a data table like this one to write your observations in. Make observations every 3–5 days. Be sure to write down if any of the sweet potato halves become rotten and need to be thrown out, and when you first see shoots on any of the halves.

After at least ten weeks, you can stop your experiment. In your lab notebook, make a data table like Table 2, below, and fill it in with your results.

For each sweet potato half, write down "Yes" or "No" to answer "Did Slips Sprout?" in the data table.

For the sweet potato halves that were not peeled, add up the total number of halves that had slips sprout on them and write this in the data table. (This would be out of a possible total of 3 since you had 3 sweet potato halves that were not peeled.) Also do this for all of the peeled sweet potato halves.

Sweet Potato

Sweet Potato Half

Did Slips Sprout?(Yes/No)

Number of Halvesthat Sprouted Slips

1

Not peeled

2

Not peeled

3

Not peeled

1

Peeled

2

Peeled

3

Peeled

Table 2. In your lab notebook, make a data table like this one to show how many sweet potato halves (peeled or not peeled) were able to sprout slips.

Make a bar graph of your results. Place the type of sweet potato half (not peeled or peeled) on the bottom of the graph (the x-axis) and the number of halves that sprouted slips on the left (the y-axis). Make a bar for the halves that were not peeled, and a second bar for the peeled halves. You can make the graph by hand or use a program like
Create a Graph to make a graph on a computer and print it.

Look at your results and try to make some conclusions.

Did some of the sweet potato halves not sprout slips? If so, which halves were they?

Did one group of sweet potato halves (the ones that were peeled or the ones that were not peeled) have more halves that sprouted slips than the other group?

What do your results tell you about what parts of a sweet potato are needed for it to make new plants?

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Variations

Instead of using sweet potatoes, you could try growing plants from regular potatoes. You can grow a new potato plant from a regular potato by putting the potato in water suspended by toothpicks, similar to what you did in this science project. Do some research into how this is usually done. If you cut a potato into many pieces, will it grow into several new plants? Are some parts of the potato more important than other parts for growing new plants?

Hormones are used by plants and animals to control growth. One plant hormone is auxin. You can buy auxin at your nursery sold as "rooting hormone." Can you do an experiment showing the effect of auxin upon tuber sprouting?

Ask an Expert

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